1. Field of the Invention:
The object of the invention is an improvement in the process of forming rolls from strips of compressible materials, particularly strips of felt with a mineral fiber base, which are designed for the thermal and/or sound insulation of buildings.
2. Background of the Related Art:
The felt strips which are made up of mineral fibers, particularly glass fibers, associated with a resin which is normally of a formo-phenolic type are used in a standard manner for the insulation of roofs, walls or floors. As the thermal resistance of a material is proportional to its thickness, modern requirements have resulted in the marketing of thicker and thicker products of between 7 and 16 cm and even of 25 cm in thickness. As glass fibers with a very low thermal conductivity and which are particularly fine have also been developed recently, strips of felt of a low density and which are thicker have to be processed.
Normally, the processing consists of coiling the strip of felt under compression so as to form a cylindrical roll, the subsequent unrolling of which is prevented by means of a paper or plastic cover. A device for carrying out this process is for example described in U.S. Pat. No. 4,583,697 in which coiling is effected in a space defined by three members: the feeding conveyor; a vertical conveyor or roller, the felt contact surface of which forms with the feeding conveyor an angle of the order of 40.degree.-80.degree., preferably in the region of 60.degree., and a compressor roller which is progressively moved away so as to increase the size of the space as the coiling operation progresses and which is driven by a rotational movement in the opposite direction in relation to the direction of feed of the vertical conveyor.
According to the teaching of the above-mentioned patent, the coiling operation is more uniform over the length of the strip if the compression applied by the the felt is not the result of a passive action but on the contrary the displacement of the compressor roller is controlled according to a predetermined program so as to impose on each turn of coiled felt a given thickness, which preferably is constant or which is reduced slightly as the coiling operation progresses. The parameters selected for the program are preferably the length of the coiled spring and its initial thickness.
By carrying out the operation in this way, a more uniform compression is achieved over the complete length of the felt strip and because of this, a more uniform resumption of the thickness after unpacking is also achieved; this makes it possible to operate with the maximum compression ratio to which the product can be subjected and to apply a simplified processing operation.
In addition to the need for a controlled compression, it is also necessary for the turns of the felt to be satisfactorily tensioned. If the felt is not correctly tensioned by the compressor roller, rolls which do not comply with the specifications are produced on industrial processing lines, the diameters of which are greater than the nominal diameter or the rolls are truncated and not cylindrical. The rolls which do not meet their specifications do not facilitate subsequent processing operations, particularly the formation of bundles and the unloading of such bundles by means of automatic systems. It has been shown in U.S. patent application No. 07/024,600 that these difficulties are essentially attributable to the surface condition of the compressor roller and in this publication it is proposed to replace the carved covering of the rubber type, which is normally used for the compressor roller, with an inorganic covering which is resistant to abrasion and which forms rough areas. This preferred covering consists of an initial layer of molybdenum deposited by Schoop's metal spraying process, onto which is deposited again by this metal spraying process a second layer consisting of grains of, for example, corundum, the thickness of which does not exceed a millimeter. In addition to these small rough areas, the surface which comes into contact with the felt is preferably provided with patterns arranged in a regular manner, of 2 to 10 mm in depth and spaced with clearances of 20 mm at the most.
A compressor roller of this type has a useful life of more than 500 hours as compared with the 150 operating hours generally obtained with rubber coverings. The wear is thus very considerably reduced and the variations in the surface condition of the roller can be controlled much more satisfactorily over a period of time so that it is possible to compensate for it at least partially by altering the speed of the compressor roller in relation to the speeds of the two conveyors, in practice by accelerating the compressor roller.
However, the results are not yet perfectly satisfactory and the greater the speed of the compressor roller, the more the shear phenonema are increased in the product and so the more it deteriorates. A deterioration of this type, even if it is held within the tolerances, does not allow the use of constant parameters. On the other hand, if it is desired to automate the subsequent operations of handling the rolls in a fairly simple manner, it is essential that their dimensions continue to be identical.
Moreover, the inventors have shown that the quality of the coiling is not in accordance with closely defined quality criteria even when the roughness of the compressor roller is perfectly constant and the compression is regulated in accordance with the teaching of U.S. Pat. No. 4,583,697. It has been observed first of all when high compression ratios of acceptable levels according to the capacity for compression of the mineral fiber and its elasticity, are applied to the leading part, the felt is damaged to a greater or lesser degree and the compressor roller splits the felt or separates the craft paper coating designed for use as a vapor shield. To overcome these difficulties the compression ratio has to be reduced so that as far as the process is concerned, some of the advantages associated with the exceptional quality of the fibers are lost.
Another disadvantage is found when coiling strips of felt, for example of 160-200 mm thickness, which are short in length (4-7 meters long). Under these conditions the thickness of the final coiled turn becomes not inconsiderable in relation to the diameter of the roll which is then of hellicoidal and not of circular section. If the positioning of the cover holding roller is not perfectly synchronized, a situation which cannot be systematically assured because of the very rapid throughputs, it can happen that the covering zone and the fixing of the cover with adhesive coincides in addition with this lack of alignment of the last coiled turn which creates a weakness in the packing.